1. Field of the Invention
The present invention relates to an image processing of a computed tomography (CT) image generated by using multi-arrayed detecting elements along a body axis, and especially to an image display apparatus and an X-ray CT apparatus for an image reconstruction processing using algorithm capable of reproducing a cone angle in the body axis direction faithfully and for clarifying a range that the image reconstruction processing is possible.
2. Description of the Related Art
In a generally employed X-ray CT apparatus, an X-ray tube and an X-ray detector with a plurality of segments (a plurality of arrayed detecting elements along a body axis direction (channel direction)) are oppositely placed to interpose an object, for example, a patient. The X-ray tube irradiates an X-ray beam to a predetermined site of the patient while rotating around the patient at “360°” together with the X-ray detector. The X-ray detector measures an X-ray dose that transmits the predetermined site of the patient as projection data. By the image reconstruction processing based on the projection data by using a computer, a CT image of the predetermined site is obtained.
There is a generally employed X-ray CT apparatus that has the X-ray detector with the segments from “2” to “64” on the body axis direction, known as “multi”, now in the world. About the generally employed X-ray CT apparatus, there is the following characteristic. When an art used in the generally employed multi-X-ray CT apparatus is just applied to an X-ray CT apparatus having an X-ray detector with “64” or more segments, there is a following problem.
It depends on a length of the segments along the body axis direction, a distance between the X-ray tube and the object, a field of view (FOV), and a cone angle, but in a case where the X-ray detector with “64” or more segments on the body axis direction is used, two areas are expected to appear on the CT image, that is, a deteriorating area caused by the relatively insufficient projection data due to the cone angle of the X-ray, and a non-deteriorating area with relatively sufficient projection data. However, when only the non-deteriorating area tends to appear on the CT image by using the generally employed multi-X-ray CT having the X-ray detector with the segments from “2” to “64”, the deteriorating area appeared on the CT image was rarely distinguished on displaying.
In a case where the deteriorating area on the CT image is intended to be masked, an operator is unable to identify a range to be masked upon CT inspection, and accordingly, fails to determine whether or not the required scan area covers the predetermined site of the patient before a scan.